How to detect the router path of traffic?

I use the ipip.net for ICMP traffic:

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I want to check the out path and back path.

such as I have A address and B address

from upper I can traceroute from A to B, then list the addresses.

but I have a question, whether the traceroute IP addresses list is from A to B's path, there can not check the B back to A's path?

3 Answers 3


Traceroute, by its nature, only reports on the path towards the target, and very imperfectly too.

You need to run traceroute from both sides to see if your routes are asymmetric.

It has to be repeated that traceroute only gives you a "sliding snapshot" of a route: the reported hops are backscatter -- the errors of many different, specific, packets failing to get where they should, and whose origins and timings may be very irregular for very many reasons. If your routes are changing, traceroute will give you only a very blurry report of what's happening, and is really only of use on your own networks where you know the range of possibilities.


The immediate and obvious answer is to hop on a remote router and traceroute back from there. I suppose you're asking though because you don't have a remote router available to you for this purpose.

It used to be that IP headers had an option to "record route (RR)", but that become a security flaw and I think get dropped most of the time now.

I think the only option for you at this point is to use sites like www.traceroute.org, which maintains a list of servers that allows public traceroutes.

  • 3
    Yes, Record Route option sometimes helps, but a) is never implemented on open networks, b) usually is limited in how many hops it will record, c) often is treated specially as it's a case of a IP packet with large header. Many ping commands implement it, but will only get answers on small, private, networks.
    – jonathanjo
    Nov 13, 2018 at 14:32

Although probably best to do a trace from both ends (as mentioned in other answers) some versions of traceroute do include a --back flag that does the following:

Print the number of backward hops when it seems different with the forward direction. This number is guessed in assumption that remote hops send reply packets with initial ttl set to either 64, or 128 or 255 (which seems a common practice). It is printed as a negate value in a form of '-NUM' .

Source: traceroute man page

  • That actually depends on the traceroute application. That option is not available on some versions/OSes.
    – Ron Maupin
    Jan 10, 2019 at 18:02
  • Edited to reflect that.
    – Eliezer P
    Jan 10, 2019 at 18:06

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